Reprocessable crosslinked polymeric compositions



United States Patent 3,267,083 REPROCESSABLE CROSSLINKED POLYMERIC COMPOSITIONS Lawrence G. Irnhof, Westfield, N..I., assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed June 7, 1963, Ser. No. 286,181 8 Claims. (Cl. 260-805) The invention relates to novel polymeric compositions. More particularly, the invention relates to novel reprocessable crosslinked polymeric compositions.

Polyolefins and olefin interpolymers, particularly the well-known ethylene polymers, are available in a Wide range of stiffness for use in divers applications such as household goods, pipe, film, wire and cable, and the like. They are characterized by thermoplasticity, the fact that they melt above their crystallization temperature, and their solubility in many organic solvents. They do, however, exhibit a variety of inferior physical properties which eliminate them from consideration for many uses for which they would otherwise be well-suited. For example, they are known to stress crack badly when exposed to various liquid environments, particularly detergents. One means used in the past to improve the physical properties of these polymers has been covalent crosslinking, and, as a result, crosslinked polymers, particularly crosslinked ethylene polymers, are well-known in the art. Crosslinking of polyolefins has been effected by use of organic peroxides and other free radical'source compounds (U.S. 2,826,570, US. 2,888,424) and by use of various methods of irradiation such as ultraviolet irradiation (I. Polymeric Sci. 22, 185 (1956); ibid., 34, 671 (1959)) and electron radiation (US. 2,855,517, US. 2,887,500 and U5. 2,906,6789). The crosslinked ethylene polymers thus produced exhibit improved solvent resistance and clarity, stress crack resistance, high molecular weight, and high viscosity. In addition, tensile properties and impact strength, over a Wide range of temperatures, are often improved.

These crosslinked polymer systems have a number of significant disadvantages. For example, an additional step for curing or vulcanizing is required. Most disadvantageous, however, is the fact that conventional crosslinked systems, such as unsaturated rubbers cured with sulfur, polyolefins cured with peroxides, and carboxylor hydroxyl-containing polymers cured with polyor difunctional covalent reagents, such as diepoxides, diisocyanates or diamines, are irreversibly, or covalently, crosslinked and cannot be reprocessed or reworked after crosslinking has been effected.

In accordance with this invention, it has now been discovered that polyolefin-based polymers containing in their backbones pendant acid groups, i.e., carboxyl or anhydride, can be reversibly, or ionically, crosslinked with certain metal oxides and polyvalent metal salts, hereinafter described in full, to provide reprocessable crosslinked polyolefin systems.

By the term polyolefin-based polymers containing in their backbones pendant acid groups" as used herein is meant an interpolymer or graft polymer of at least one monoolefin preferably containing from 2 to 10 carbon atoms inclusive, with at least one acid group-containing, i.e., carboxylor anhydride group-containing, monoolefinically unsaturated monomer.

ice

The polyolefin-based polymers containing pendant acid groups contemplated for use in this invention are high polymers, i.e., normally solid, high molecular weight polymers, and are to be distinguished from those polymers normally considered to the Waxes or greases. The melt index of useful polyolefin-based polymers can range from a melt index of 0 to about 1000, and preferably from about 0.02 to 100.

Illustrative of polyolefin-based polymers containing pendant carboxyl or anhydride groups which can be reversibly crosslinked to provide the reprocessable polymeric compositions of this invention are ethylene/ acrylic acid copolymers, ethylene/methacrylic acid copolymers, ethylene/ethyl acrylate/acrylic acid terpolymers, ethylene/vinyl acetate/acrylate acid terpolymers, and polyethylene/maleic anhydride graft polymers prepared by modification of polyethylene with maleic anhydride under conditions of chain scission as are produced by combining the molten reactants, and the like. This list however, is intended to be merely illustrative and should not be considered restrictive of the polyolefin-based polymers containing pendant acid groups which can be used. It is to be emphasized that any polymer containing a hydrocarbon backbone possessing pendant carboxyl or anhydride groups can be successfully employed herein. The preferred polyolefin-based polymers containing pendant acid groups are ethylene/acrylic acid and ethylene/vinyl acetate copolymers and ethylene/ethyl acrylate/ acrylic acid terpolymers.

The concentration of aicd groups in the polyole-finbased polymers can be from 0.1 percent by weight, calculated as free carboxyl group, to 15 percent by weight. The preferred range is from 0.5 to 10 percent by weight carboxyl.

Crosslinking agents which, when crosslinked with the above-described polyolefin-based polymers containing pendant acid groups provide reprocessable crosslinked polymeric compositions, are polyvalent metal alkanoates containing from 3 to about 12 carbon atoms in the alkane chain, e.g., hexanoates and octanoates, and the like, and polyvalent metal salicylates, naphthenates, oxides, hydroxides, and acetyl acetonates. The polyvalent metal alkanoates, salicylates, naphthenates and acetyl acetonate which can be used are salts of those metals from Groups IIA and HE, Group IIIA, preferably aluminum, IVA and IVB, preferably tin and Zirconium, VIB, preferably chromium, and VIII, preferably iron and nickel, of the Deming Periodic Table (Handbook of Chemistry and Physics, 30th edition, p. 312). Polyvalent metal oxides and hydroxides useful herein are those metal oxides and hydroxides of Group II, preferably zinc and magnesium, of the Deming Periodic Chart.

From about 0.05 to 120, and preferably from about 0.2 to 15, parts of the crosslinking agent can be used per parts polyolefin-based polymer containing pendant acid groups, by weight.

The reversibly crosslinked polymeric compositions of this invention cover a spectrum of stiifness down to and including the elastomeric range, i.e., from about 100 to about 150,000 p.s.i. as determined by ASTM D63858T.

The crosslinking agent can be mixed with the polymer by any method which provides an eificient combination, such as mixing in a Ban'bury mixer, mixing solutions of the polymer and crosslinking agent, dry blending where applicable, and similar mixing techniques. The curing time and temperature are similarly not particularly critical, and can vary over a wide range. In general, temperatures from about 75 to 250 C. are satisfactory, depending on the reactivity of the reagent used. Time for curing depends upon the temperature used, increasing as the temperature decreases.

In a typical mixing and curing operation, the fluxed sheet of polymer plus crosslinking agent was compression mold cured at a temperature of about 180 C. for 30 minutes. At this temperature for this period of time maximum reaction had almost always occurred. Frequently, however, the mixing step produced the maximum crosslinking for a specific system. In actual prac tice, the curing step is carried out either in the mixing step or the extrusion or molding operation.

It is to be emphasized that the polyolefin-based polymers of this invention are reversibly crosslinked. Reversible crosslinking cannot be effected with polyolefins and olenfin copolymers which do not contain pendant acid groups. Reversible crosslinking is to be clearly distinguished from the irreversible crosslinking obtained with free radical-generating crosslinking agents. The reversibly crosslinked polymers of this invention can'be readily Worked and formed on heating and behave as thermoplastics whereas irreversibly crosslinked polymers contain infusible and non-reworkable chemical bonds. Especially preferred in preparing reversibly crosslinked terpolymer formulations are the polyvalent metal oxides, zinc oxide and magnesium oxide, and octoates such as zirconium octoate, barium octoate, chromium octoate and nickel octoate, as well as zirconium salicylate, zirconium naphthenate, zirconium acetyl acetonate, aluminum acetyl acetonate, and zinc acetyl acetonate. The great advantage of the use of reversible crosslinking agents is that they impart to the crosslinked polymer the ability to be reprocessed at the high temperature and pressure used in most fabricating techniques for thermoplastics. Because these crosslinked polymer systems can be reprocessed they are useful in techniques such as injection and blow molding, and monofilament extrusion, where crosslinked systems have heretofore not been applicable. Other advantages are that scrap can be reworked, thus providing considerable product economies, and that simplification can be made in techniques that generally have required a curing step following the forming step (such as compression molding, and extrusion of wire or cable followed by passage through a continuous steam vulcanizer to effect cure).

Without absolute commitment to this theory, it is believed that the reprocessability of these reversibly crosslinked systems is due to the mobility of the ionic link in the presence of free carboxyl groups on the terpolymer chain when it is subjected to high stress (pressure) at a high temperature. The ionic crosslink breaks and the metal ion, still attached to one polymer chain, slips along until the stress is released. When the stress is released, the metal ion reacts with a nearby free carboxyl group, thereby reforming the crosslink and restoring the good physical properties and high temperature solvent resistance which are characteristic of crosslinked materials. These reversibly crosslinked systems also show similar tensile strengths at elevated temperatures and similar stiffnesstemperature relationships as do irreversibly crosslinked copolymers.

The reprocessability of reversibly crosslinked polymers described herein has been shown by measurement of melt flow rates and by repressing compression molded plaques. The repressed plaques show almost the same properties as do the original plaques. Where there is a small decrease in some of the properties it is thought to be. due to the fact that fewer ionic crosslinks reform in the repressed polymer as compared with the number present in the original crosslinked polymer. The steric effect of other pendant groups or a cage effect which may include metal ions could account for the reformation of fewercrosslinks.

Polyvalent metal oxides, such as zinc oxide and mag nesium oxide, yield reprocessable systems when used as "additives to the polyolefin-based polymers described here- .in. The mechanism leading to reprocessab ility is thought to be different from the ionic mechanism described earlier. These oxides do not appear to form ionic crosslinking bonds themselves; the reinforcement effected in their formulations may be due to hydrogen bonding with free carboxyl groups. Inasmuch as a reinforcement found with no other filler is achieved, however, such polyvalent metal oxides are best considered reactive fillers. These reactive fillers can be used in greater amounts than the crosslinking agents normally used for crosslinking, e.g. from about to 150 per hundred parts polymer, by weight, if desired.

A great number of common fillers are accepted with ease by the reversibly crosslinked polymers of this in,

vention; examples of such fillers include carbon blacks, clays, magnesium silicate and silica. The curing formulation can also contain stabilizers, antioxidants, processing aids, colorants, and other additives if desired.

In the reprocessable polymeric compositions of this invention cure proceeds rapidly during the forming step, and the customary post-forming vulcanization operation associated with peroxide-crosslinked polymer systems can be omitted. In addition, at the temperatures and pressures normally encountered in end-use, the products herein exhibit the highly advantageous physical and mechanical properties typical of irreversibly cross-linked materials but can readily be reprocessed and reshaped at higher temperatures and pressures, and without the serious physical property deterioration associated with reprocessed peroxide-crosslinked systems. In general, the reversibly crosslinked polymers of this invention exhibit superior resistance to solvents, resistance to distortion at elevated temperatures, elevated temperature tensile strength, stress crack resistance, and other properties heretofore found only in polymers crosslinked irreversibly with peroxides and the like. The polymers described herein are, therefore, useful in applications found by irreversibly crosslinked polymers such as pipe, cable jacketing, line wire covering, power cablev insulation, and the like.

To illustrate the invention more fully, the following descriptions and examples are given. All parts and percentages are by weight unless otherwise specified.

Physical properties were measured on samples using the following test methods:

Test: ASTM No.

Ultimate tensile and percent elongation D-412-51T Vicat softening point D1525-58T Tensile impact strength Tensile set at 100% elongation D-470 Secant modulus of elasticity D-638-5 8T Environmental stress crack resistance Melt index D123857T in Izod testing machine is used to run this test. The test specimen, in the form of a x 2 x 0.040 plaque is mounted in a horizontal position in a device consisting of two clamps. One clamp is stationary and the other is free permitting horizontal travel, After the sample is. mounted, a calibrated pendulum is allow to strike the free clamp. The momentum of the pendulum drives the clamp along a horizontal path, thus elongating the sample. The force, in foot pounds per square inch, required to break the sample is then cal ci i llated. t

e cs specimen is the A die siz a ASTM 13 412. e, s described in To determine stress crack resistance, a mil compression molded specimen 0.5 x 1.5" was slit along the long dimension. The slit was 20 mils deep and 75 mils long. The specimen was then bent 1S0". Ten such bent specimens were held 1n a channel which was then immersed in Hostapal, a. non-ionic surfactant believed to be similar to nonyl phenoxy polyethylene ethanol, at 50 C., in a test tube. Two such channel devices were put into each tube, providing 20 speci mens per test. Time to failure of any one spec imen was the appearance of a crack perpendicular to the slit; Ted is the time to failure of 50 per cent (i.e., 10) of the specimens.

5 EXAMPLE 1 Example 1 describes various polyolefin-s containing in their backbones pendant acid groups and presents examples of processess well-known in the art, by which these polymers can 'be prepared. serving to describe these polymers. Code letters A-R In "Fable 1 is compiled data 5 6 EXAMPLE 2 will be employed hereinafter in the examples to refer to is seen that polyvale-nt metal loctoates, salicylates, napha particular polymer.

thenates, oxides (and hydroxides), and acetyl acetonates Table I.Ply0lefin descriptions Code Process for Preparation Melt Flow Percent by Weight 00- Modulus Letter Index Index monomer in Product EIHYLENE/ACRYLIC 11cm COPOLYMER. GROUP 1 Copolymerization, tubular proc 4. 0 200 4. 3 45, 000 do 25 31 13. 5 44,100 9. 4 580 2. 4 55, 900 Copolymerization, stirred autoclave proc 8.2 300 3. 8 41, 000 Copolymerization, tubular proc 17 7. 2 45, 000 ..do 79. 2 1, 000 4. 6 45, 000

Percent Percent by Weight by Weight ethyl acrylic ETHYLENE/ETHYL ACRYLA'lE/ACRYLIC ACID TERPOLYMER; acrylate acid GROUP 11 Partial hydrolysis of ethylene/ethyl acrylate copolymer (tubu- 1. 6 98 11 4.0 5, 700

lar process). .do 25 425 20 4. 2 800 .do. 3. 5 156 3-5 2.1 12, 400 Almost complete hydrolysis of ethylene/ethyl acrylate copoly- 2. 5 137 1 1.3 15, 400

mer (tubular process). do .7 1 7.8 12,700 Partial hydrolysis of ethylene/ethyl acrylate copolymer (tub- 52 1-2 5. 8 14, 400

ular process). Direct tubular polymerization 13 200 17 6.9 2, 700 Almost complete hydrolysis of ethylene/ethyl acrylate copoly- 2. 2 82 1 3. 5 11, 000

mer (tubular process).

Percent by Weight vinyl ETHYLENE/VINYL ACETATE/ACRYLIC ACID TERIOLYMERC acetate GROUP 111 O Direct stirred autoclave polymerization .27 33 10.6 5.1 10, 000 1? do 3. 7 170 38. 6 3. 3 750 Percent by Weight 00- POLYE'IHYLENE/MALEIC ANHYDRIDE GRAFT POLYMER: monomer in Product (moor rv Maleic anhydride graft polymerized onto 0.95 density, 0.2 melt 08 37 0. 5 65, 500

index high pressure polyethylene. Maleic anhydride graft polymerized onto 0.92 density, 0.7 melt 1 30 1. 0 22, 900

index high pressure polyethylene.

Table ll.-Crosslinking agents for ethylene/acrylic acid copolymers Uncrosslinked Polymer Crosslinked Polymer Properties Parts per Crosslinking Agent Hundred Curing parts Melt Flow Percent Melt Flow Polymer Polyolefm 11 Index Index Gel Index Index Temp., Time,

0. min.

Stannous octoate Z 14.0 A- 4. 0 200 180 30 Chromium octoate 24. 6 A 4. 0 200 180 30 Ferrous octoate 24.6 A 4.0 200 180 30 Zirconium octoate 10.0 B 0.25 31 15 Zinc octoate 8. 8 C 9. 4 580 180 30 Calcium octoate 20.0 A 4.0 200 220 30 Zirconium salicyla 9. 3 A 4.0 200 180 30 Zinc oxide- 16. 0 B 0. 25 10 Magnesium 0x 5. 0 C 9. 4 580 30 Aluminum-acctyl ac 10. 0 A 4. 0 200 180 15 Zirconium acetyl acetonate 9 14.6 A 4. 0 200 180 30 1 Acrylic acid content determined either by KOH titration oi free acid or by elemental oxygen analysis.

2 25.0% by Weight tin.

3 6.4% by weight chromium.

4 6.6% by weight iron.

5 19.2% by weight zirconium.

5 22.0% by weight zinc.

7 5.0% by weight calcium.

8 20.6% by weight zirconium.

9 12.0% by weight zirconium.

(1)1 0 extrliligion (i.e., resin too viscous or stiff to extrude at the pressure and temperature of the test; values usually less than .001 or gms. min.

11 See Table I for description of polyolefin.

provide metal salt 'cros-slinking which is characterized by To determine percent gel, a 0.3 gram piece of the cured reprocessability, freedom from the usual post-forming sheet was placed in a 100 mesh copper Wire cage and vulcanization, and reworkability of material. In Table immersed in refluxing ethyl benzene for 16 hours. The II above, and in Tables III and IV following, the efiec-t of cage was then dried at 110 C. for 3 hours. The weight the curing agent is noted by increase in percent gel and 5 of the resin remaining in the cage was the gel.

decrease in melt or flow index compared with the uncured EXAMPLE 3 control samples.

Example 2 and Example 3 following, illustrate in par- Exa ple 3 sho crosslillking f ethylene/ethyl yticular the effectiveness of oxides of metals of Groups late/ acrylic acid terpolymers and ethylene/vinyl acetate/ IIA and KB in peducing melt o flow i d (inrcpreasing acrylic acid terpolymers with crosslinking agents leading viscosity) and in increasing crosslinking (as measured by to reprocessable crosslinked polymeric compositions. increased percent gel), especially when the oxide is used at f r Example 3 is complied in Table III.

Table III.Crosslinking agents for terpolymers Uncrosslinked Control Cure Conditions Cured Data Crosslinking Agent (Parts per Hundred Parts Polymer) Polymer Percent Flow Temp., Time, Percent Flow Code 00011 Index 0. (min.) Gel Index ETHYLENE/ETHYL ACRYLATE/ACRYLIC ACID TERPOLYMERS Zirconium octoate (10.5) G 2. 98 160 30 Zinc octoate 2 (12.2) G 2. 5 98 180 30 Zirconium naphthenate 3 (21.0) G 2. 5 98 140 Zinc oxide (5.0) H 2. 6 425 180 30 Magnesium oxide (5.0) H 2. 6 425 180 30 Calcium oxide (11.2) N 2. 2 82 180 60 Zinc acetyl acetonate (146)-..- G 2. 5 98 180 30 Aluminum aeetyl acetonate (12. G 2. 5 98 180 30 Zirconium acetyl acetonate (28.0) G 2. 5 98 180 30 Chromium octoate 4 (12.2) I 1. 30 156 180 30 Ferrous octoate 5 (122)--.. I 1. 30 156 180 30 Zirconium salicylate 6 (6.8) I 1. 30 156 180 30 Stannous oetoate (7.0) L--. I 1. 30 156 180 30 Nickel octoate (11.7) B I 1. 30 156 180 30 ETHYLENE/VINYL ACETATE/ACRYLIC ACID TERPOLYMERS Chromium octoate P (3.3) 0 3. 2 33 160 37 1. 4 Zinc oxide (100.0) P 2.1 170 150 0 20 1 19.2 percent by weight zirconium.

2 20.0 percent by weight zinc.

3 12.0 percent by weight zirconium.

4 6.4 percent by weight chromium.

6 6.6 percent by weight iron (II).

20.6 percent by weight zirconium.

7 25.0 percent by weight tin.

8 5.0 percent by weight nickel.

6.4 ercent by weight chromium.

The number in parentheses following the name of the erosslinking agent 15 the parts of crosslinking agent.

as a reactive filler, i.e., is used in large quantities, e.g., EXAMPLE 4 10450 Parts Per hundred Part Polymer Example 4 shows crosslinking of polyethylene/maleic In these and ub5equent examples: the resln w fluxed anhydride graft polymers with crosslinking agents leading on a two-roll mill at about C. and the additives were t e ble lcrosslinked polymeric compositions.

then milled in. Milling time was approximately ten Data for Example 4 is compiled in Table IV.

Table IV.Cr0sslinking agents for polyethylene/malez'c anhydride graft polymers Uncrosslinked Control Cure Conditions Cured Data Crosslinking Agent (Parts per Hundred Parts Polymer) Polymer Percent Flow Temp., Time Percent Flow Code Maleic Index 0. (min) Gel Index Anhydride Zinc oxide (20) R 1.0 .30 180 30 75 N.E. Zirconium octoate (19.2% Zr) (8) R 1.0 30 180 30 82 N .E. Do 0. 5 37 30 61 20 minutes, including ten end passes to dispense the additives. EXAMPLE 5 Compression molded plaques (20 or 75 mil thickness) were made and the plaque was cured in the mold at the designated temperature and time.

Example 5 shows the effect and range of concentration of crosslinking agent. Data for Example 5 is compiled 75 in Table V.

Table V.Efiect of concentration of crosslinking agent Initial Resin Curing Crossllnked Properties Crosslinking Agent (Parts per Hundred Parts Polymer) Resin Flow Time, Temp, Gel, Flow Code Index min. C. Percent Index Zirconium octoate 1 (0.5) I 156 180 30 8 80 Zirconium octoate 1 (1.0) I 156 180 30 26 51 Zirconium octoate 1 (2.0) I 156 180 30 41 2. 6 Zirconium oetoate (6.0) I 156 180 30 62 0.9 Zirconium octoate (20.0) G 98 180 30 65 2.1 Zirconium ootoate 1 (25.0) D 300 180 30 50 3. 6 Zinc oxide (50.0) G 98 180 30 0 .01 Chromium octoate 2 (0.78)-. O 33 160 2 Chromium octoate 2 (1.56). O 33 160 15 3.0 Chromium octoate 2 (3.1) O 33 160 15 37 1. 4 Zinc oxide (100.0) P 170 150 0 20 Zinc oxide (100.0) H 425 150 20 60 N .E.

1 20 percent by weight zirconium. 2 6.4 percent by weight chromium.

EXAMPLE 6 Example 6 illustrates the effect and range of carboxyl content and comonomer concentrations, and melt i-ndices of uncured polymers. Resins codes I, Q, P, and B illustrate polymers of varying carboxyl content, and polymers codes B, G, H, and P demonstrate crosslinkability of polymers containing up to about 40 percent by Weight of a non-carboxyl group containing comonomer. Resins codes Q, E, J, and F show examples of varying melt indices of base polymers. Data for Example 6 is compiled in Table VI.

Table VI.Efiect of resin variables EXAMPLE 7 Percent Crosslinker Resin Code Ethyl Percent Melt Flow Percent Acrylate COOH Index Index Gel or Vinyl Reagent Ihp Acetate 0 0.8 2.5 0 0 0 .8 Zr. Oct. 10 0.33 16 0 2 0.5 .08 37 9 2 0.5 Zr. oct. 8 N.E. .20 61 D 2 .6 79 0 0 2 .6 Zr Oct. 10 16 25 0 8 .5 .25 31 8 0 Zr oct. 10 .1 7 52 3 11 2 .5 98 0 11 2.5 Zr oct. 10 N.E. .06 65 a 20 2.6 25 425 0 3 20 2.6 Zr oct. 9 .13 86 4 38.6 2 .1 3.7 170 0 4 38.6 2.1 Zr oct. 10 0.45 20 O 4.5 .17 30 0 4.5 Zr oct. 10 N.E. N.E 43

1 Parts per hundred parts polymer. 2 Percent by weight maleic anhydride (by infrared). a Ethyl Acrylate.

1 Vinyl Acetate.

an ethylene-acrylic acid copolymer (Code B), and on uncured controls of these polymers.

Table VII.Physical properties of crosslin ked ethylene/ ethyl acrylate/acrylate acid 1 terpolymers Crosslinking Agent (Parts Resin Per- Tensile Tensile Elon- Yield Strength Secant Flow per Hundred Parts Polymer) Code cent Impact Strength, gation, Strength, at 100 0., Mod., Index Gel p.s.i. percent p.s.i. p.s.i. p.s.i.

Control (0) G 0 550 2, 300 650 685 0 5, 740 9B Zirconium octoate (10.5) G 603 2, 190 365 1, 610 170 5, 380 .06 Control (0) M 0 260 440 210 440 2,700 200 Zirconium octoate (10) M 51 365 8 0 220 820 2, 630 20 Control L 0 702 3, 420 575 3, 420 46 14, 440 52 Zirconium octoate (15). L 60 580 2, 280 460 1, 895 390 11, 450 .07 Zinc acetyl acetonate (13 .6) L 18 354 2, 900 375 1, 510 280 24, 040 2 Control K 0 830 3, 300 565 960 270 12, 730 45 Zirconium octoate (16 .6) K 640 2, 660 465 1, 250 440 12, 160 2 N.E. ontr I 0 387 1, 760 450 1, 210 110 16, 200 156 Zirconium octoate (10 5)- I 60 460 1, 660 550 1, 030 540 12,900 6 .6 C011 B 143 2, 300 1, 790 360 44, Zinc oxide (16 .0) B 1 7 3, 620 0 3, 620 1, 450 90, 400 N.E.

1 The curing reaction using zirconium octoate and zinc oxide is complete by pressing at C. or 10 minutes; acetonates are complete at about C.

2 No extrusion.

1 l l 2 EXAMPLE 8 Table- IX.Imprved stress crack resistance by crosslinking Example 8 illustrates the variety of fillers which can be successively accepted by the reprocessahle crosslinked Cmssnnking Agent (Parts Per Hundred Number Of Parts Polymer) Breaks per F60 systems of this invention. Data for Example 8 is com- 5 20Samp1es piled in Table VIII. Ethylene/ethyl acrylate/aerylic Zlrconium octoate() 1 3wks. acid terpolymer was used as the oanboxyl group-containing Zinc oxide (20) 0 3 wks polyolefins in this ex 16. Control, Polymer Code G (0) 20 8 hrs From Table VIII it can be seen that when the ter- 10 EXAMPLE 1O polymer is crosslinked with 20 parts per hundred of ter- Example 10 illustrates the reprocessability of the repolymer, .b i h w fl w index was decreased flr versibly cured polymers of this invention. The physical properties of the cured systems compression molded a 98 to 0.27. A control copolymer of ethylene and ethyl Second time are essentially as good as the Physic 31 pm? y the other hand, when mixed with 33 Parts erties of those cured systems compression molded only zinc oxide per hundred parts of resin, remains virtually 01108- Comparable wvalehfly crosslinkqd y for unchanged in melt index This example illustrates the example, those cured with dianisidine diisocyanate, and

polyolefins, for example polyethylene, cured with peroxcombmed cr'osslmkmg/filhng funotlon Served by metal ides, cannot be remolded or extruded after cure to provide oxides. I a polymeric system having good properties. The poor Table VIIl.Filled vulcanizates 1 Filler and Crosslinking Agent (parts Resin Percent Tensile Tensile Elong., Yield Tensile Secant Flow Brittle per hundred parts polymer) Code Gel Impact Str., percent Strength, Strength, Modulus, Index Temp.,

p.s.i. p.s.i. 100 C. p.s.i. C.

ETHYLENE/ETHYL ACRYLATE/ACRYLIC non) TERPOLYMER Control (0) K 0 880 3,300 565 960 270 26,980 (40) Clay plus (13) Zirconium octoato K 75 860 2, 280 325 1, 440 590 24, 580 Zinc oxide (1 K 94 140 2, 940 140 2, 290 455 Control (0) G 0 550 2, 300 650 5 0 5, 740 Zinc oxide 5 G 58 540 3, 270 300 3, 270 355 13,000 (40) Clay plus (10 G 71 405 1, 750 400 1,190 120 10,780 Zine oxide (20) G 0 522 3, 810 465 3, 810 200 10, 510 Control (0) H 0 430 270 275 170 O Zinc oxide H 0 300 2, 900 495 570 210 2,050 Zmc oxide (150) H 2,800 550 5, 700 Control (0)- L 0 700 3, 420 575 8, 420 50 14, 440 Carbo plus (16) Zirconium octoate L 83 2,060 70 2,060 570 48,600 .04

1 Compression molded at 180 0. for 30 minutes unless otherwise stated. 1 Molded at 120 0., 15 minutes. 3 Too soft.

EXAMPLE 9 tensile properties, poor impact strength, and brittleness of the remolded covalently crossli-nked systems are espe- Example 9 illustrates the improvement In stress crack i ll t th i hi connection resistance gained by use of the reprocessable crosslinked n Table X is compi d data shown g reproeessability In Table 1X is compiled data 50 of reversibly crosslinked ethylene/ethyl acrylate/acrylic f my x 1 acid tenpolyrner. In Table XI is presented similar data e m for reversibly crosslinked ethylene/ethyl acrylate copolymer, and in Table XII is compiled data for reversibly crosslinked polyethylene/maleic anhydride graft polymer.

systems of this invention.

Table X.-Repr0 cessability of crosslinked ethylene/ethyl acrylate/acrylic acid tea/polymer Tensile Prop, 23 C. Tensile Prop, 100 C. Crosslinking Agent No. of Per- Brittle- Mod- Rosin (Parts per hundred Presscent Tensile ness, ulus, Code parts polymer) ings Gel .Flow Strength, Elon- Yield, Strength, Elon- Yield, Impact Temp, p.s.i.

Index p.s.i. gation, p.s.i. p.s.i. gation, Percent 0.

Percent Percent Zirconium octoate (20). 1 87 2, 640 415 1, 390

mate 1 (7.8). 2 83 675 30 675 D'lcumyl Peroxide (4) 1 88 2, 380 395 2, 380

-.do 2 83 l, 380 1, 380

' The first pressing would have properties similar to the zirconium 1 Poor.

octoate cured compound using same base resin. 3 0.918 density, 2 melt index, high pressure process Table XI .Reprocessability of polyvalent metal salt crosslinked ethylene/ acrylic acid copolymers 1 Per- Tensile Prop., 23 0. Processing cent Flow Mod- Tensile Gel Index ulus Impact Str. Elong. Yield Press-cured 2 one time 43 40, 400 2, 050 140 1, 690 138 Repressed 3 45 1, 990 180 1,800 155 Control 37 38, 800 1, 920 85 1, 540 94 l Resin Code E.

2 10 parts zirconium oetoate used per hundred parts polymer; cured 180 C. {or 30 minutes.

Press-cured plaque broken, pieces plied, then compression molded again at 180 C. for minutes.

Table XII.Repr0cessobility of crosslinked polyethylene/ maleic anhydride graft polymer Curing Tensile Prop.

Crosslinking Agent (Parts per Resin I Elem Percent Flow Tensile Modulus hundred parts polymer) Code Temp, Time, Strength, anon Gel Index Impact 0., min. p.s.i. g

percent Control (0) R 180 15 2, 050 400 26 .31 250 24, 300 Zinc oxide R 180 30 1, 730 200 75 NE. 260 22, 600 Zirconium octoate (8) R 180 30 2,100 230 82 N.E. 330 13,700 Zirconium octoate (repressed) (8) R 180 15 2, 030 100 82 NE. 370 16, 400 Control (0) Q, 180 150 3, 420 100 37 57 65, 500 Zirconium octoate (8) Q 180 30 2, 910 61 .20 102 81, 900 Zirconium octoate (repressed )(8) Q 180 15 3, 320 85 52 I06 118 81, 400

EXAMPLE 11 metal alkanoate containing from 3 to 12 carbon atoms in To demonstrate the reprocessability of the reversibly crosslinked polymers of this invention still further, metal salt-crosslinked polymers were, after having been presscured, extruded through a batch extruder, having the barrel of the conventional melt indexer described in ASTM D-123 8-57T, a melt index die, and having a motor driven ram operable up to about 15,000 p.s.i. An ethylene/ethyl acrylate/acrylic acid terpolymer (Code 1) containing 15 parts nickel octoate (5% nickel), for example, was satisfactorily extruded at a pressure of about 2,000 p.s.i.

In Table XIII is presented data for four crosslinked of polymers of this invention, compared with a peroxide cured control. All samples retained their original degree of crosslinking (percent gel) after the high stress-high temperature conditions were removed.

Table XIIL-Extrusion 0f reprocessable crosslinked ethylene polymers 1 0.918 density, 2 melt index, high pressure process.

What is claimed is:

1. Reprocessable crosslinked polymeric composition comprising per 100 parts by weight of polyolefin-based polymer having a melt index of from about 0 to 1000 and containing in its backbone from about 0.1 to 15 percent by weight, calculated as free carboxyl group, of pendant acid group selected from the group consisting of carboxyl and anhydride, from about 0.05 to 150 parts by weight of crosslinking agent selected from the group consisting of polyvalent metal alkanoates containing from 3 to about 12 carbon atoms in the alkane chain, salicylates, naphthenates, and acetonates, said polyvalent metal being selected from the group consisting of metals of Groups IIA, IIB, IIIA, IVA, IVB, VIB, and VIII of the Deming Periodic Table.

2. Reprocessable polymeric composition claimed in claim 1 wherein the crosslinking agent is a polyvalent References Cited by the Examiner UNITED STATES PATENTS 2,649,439 8/1953 Brown. 2,849,426 8/ 1958 Miller. 3,178,389 4/1965 Hallenbeck 260-41.5

MORRIS LIEBMAN, Primary Examiner.

I. S. WALDRON, Assistant Examiner. 

1. REPROCESSABLE CROSSLINKED POLYMERIC COMPOSITION COMPRISING PER 100 PARTS BY WEIGHT OF POLYOLEFIN-BASED POLYMER HAVING A MELT INDEX OF FROM ABOUT 0 TO 1000 AND CONTAINING IN ITS BACKBONE FROM ABOUT 0.1 TO 15 PERCENT BY WEIGHT, CALCULATED AS FREE CARBOXYL GROUP, OF PENDANT ACID GROUP SELECTED FROM THE GROUP CONSISTING OF CARBOXYL AND ANHYDRIDE, FROM ABOUT 0.05 TO 150 PARTS BY WEIGHT OF CROSSLINKING AGENT SELECTED FROM THE GROUP CONSISTING OF POLYVALENT METAL ALKANOATES CONTAINING FROM 3 TO ABOUT 12 CARBON ATOMS IN THE ALKANE CHAIN, SALICYLATES, NAPHTHENATES AND ACETONATES, SAID POLYVALENT METAL BEING SELECTED FROM THE GROUP CONSISTING OF METALS OF GROUPS IIA, IIB, IIIA, IVA, IVB, VIB, AND VIII OF THE DEMING PERIODIC TABLE. 